Butterfly Grove

Pismo State Beach Monarch Butterfly Grove

A group of orange and black monarch butterflies rest on a green tree branch.

The Pismo State Beach Monarch Butterfly Grove is a publically owned, protected overwintering site for western monarch butterflies.   Monach clusters are found in over 200 coastal sites, including several sites in San Luis Obispo County. 

The Pismo State Beach Monarch Butterfly Grove generally has one of the largest overwintering western monarch populations.  The current monarch population is threatened.  Recent counts show a 90% drop from counts done 25 years ago. 

Why do they migrate to coastal california?

Monarchs seek places with ideal microclimates for their winter habitat.  They require a sheltered area buffered from cold temperatures, storm, and wind.  The coastal environment provides adequate moisture and some nectar plants. 

At the Pismo State Beach Monarch Butterfly Grove, the tall eucalyptus and Monterey cypress trees provide the shelter and canopy for thermal stability. Although cool temperatures are needed to slow the use of stored energy reserves, monachs cannot survive long periods of freezing temperatures.  Unusually warm temperatures trigger a search for food and mates.  

The Amazing Monarch Migration

What's unique about monarch migration? 

The western monarchs in the grove are four generations removed from the last year's overwintering monarchs.  Monarchs can reach high altitudes and travel as far as 200 miles a day.  Western monarchs don't travel in a mass migration. 

Where do they come from?

Monarchs spend summers as far north as Canada. With the approach of winter, the late summer and fall butterflies head south or west to their overwintering grounds.  Because they cannot tolerate extreme cold winter temperatures, monarchs west of the Rocky Mountains come to coastal California.  Monarchs east of the Rocky Mountains overwinter in the mountains of central Mexico or along the Gulf Coast.  Some may travel as far as 2,000 miles to reach these sites.

How do they find their way?

Studies indicate that sensors in the monarch's antenna are key to migration, providing information about the time of day the same way a clock does.  Reseachers theorize that this information, combined with information about the sun's postion, is key for navigation.  On overcast days monarchs use a UV light-triggered geomagnetic compass as a backup navigational system. 

Providing for the Future

Unfortunately, the remarkable monarch butterfly annual migration is threatened.  Development of land on overwintering sites, loss of milkweed, extreme weather events, and even climate change are impacting the eastern and western monarch populations.  University-based studies are helping scientists understand more about the behavior and life patterns of these fascinating creatures. 

Be Monarch-Friendly

In the Grove:

  • Watch for butterflies on the ground. Don't step on them!
  • Stay on designated paths.
  • Do not disturb butterfly clusters.
  • Dispose of all litter in proper receptacles.

At Home:

  • Minimize use of herbicides, insecticides, and fungicides.
  • Plant milkweed away from overwintering habitats.
  • Plant native nectaring flowers.
  • Check with your local nurseries for native milkweed varieties. 
  • Support conservation efforts.
  • Educate yourself on monarch conservation efforts: